What type of immunity occurs when a pregnant woman is vaccinated with Tdap?

When a pregnant woman is vaccinated with the Tdap vaccine during her pregnancy, she develops antibodies in response to the components of the vaccine. These antibodies can cross the placenta and subsequently be transmitted to her fetus. This process provides the newborn with immediate, temporary immunity to certain infections, such as whooping cough and tetanus, until they can receive their own vaccinations.

This type of immunity is categorized as passive immunity because it involves the transfer of antibodies from one individual (the mother) to another (the child), rather than the child's immune system generating the response itself. Passive immunity does not involve the host's immune system creating a long-lasting defense against the pathogens, as would occur with active immunity, where the body produces its own antibodies in response to an antigen through vaccination or natural infection.

In this scenario, since the immunity conferred to the fetus is derived from the mother's vaccination and not from the fetus's own immune response, passive immunity is the correct classification.